In the production of oil and gas using a wellbore, safety valves are almost always required to be installed within the wellbore. The safety valves are designed to isolate the wellbore in the event of an operational condition that can result in damage at or near the surface. The operation of safety valves can become problematic in deep-water wells, where thousands of feet of hydrostatic pressure can build up even before entering the wellbore. Existing safety valves operate using hydraulics, Nitrogen, and/or magnets.
Some conventional hydraulic safety valves may have limited setting depths unless nitrogen balance pressures are used to offset the effects of high head pressures. The deeper a conventional safety valve is set, the higher the forces will be acting on the hydraulic piston. Eventually, the fail-safe power spring used to return the flow tube (and allow the flapper to close) may not be strong enough to lift the column of fluid acting on the hydraulic piston. Nitrogen has been used in the past to offset this effect. However, valves designed with nitrogen charge pressure may have the added disadvantage of operational variation with temperature and the potential of lost gas pressure.
Some conventional hydraulic safety valves also may have slow closure response times. When the hydraulic pressure is relieved on the safety valve (in an emergency condition), the time required to move the hydraulic fluid through the small diameter control line could be longer than desired. This presents operational, and sometimes regulatory, risks during operation.
Existing electric safety valves have significant power requirements to either drive motors, or hold solenoids in position to function properly. High power requirements generate significant heat which results in waste and may lead to premature component failure during the life of the well.
Therefore, there is a need for an improved safety valve system to solve the problem of hydrostatic pressure and depth limitations as well as minimize the power required to operate electric safety valves. By using an electric actuator and eliminating the need for a hydraulic control line, problems associated with depth and pressure can be mitigated. Slow response time is also mitigated because the safety valve is able to close almost instantaneously. Further, power required to hold open such safety valve system is reduced, in turn reducing component failure and power waste.